The Section is conducting patient-oriented research about the etiology, pathophysiology, genetics, diagnosis, and treatment of pheochromocytoma (PHEO) and paraganglioma (PGL). Projects include not only translational research-applying basic science knowledge to clinical diagnosis, pathophysiology, and treatment-but also reverse translation research where appreciation of clinical findings leads to new concepts that basic researchers can pursue in the laboratory. In order to achieve our goals, the strategy of the Section is based on the multidisciplinary collaborations among investigators from multiple NIH Institutes and outside medical centers. Our Section links together a patient-oriented component with two bench-level components. The patient-oriented component (Medical Neuroendocrinology) is currently the main driving force for our hypotheses and discoveries. The two bench-level components (Tumor Pathogenesis and Chemistry & Biomarkers) emphasize first, technologies of basic research tailored for pathway and target discovery and second, the development of the discoveries into clinical applications. Clinical aspects of PHEO/PGL Measurements of plasma metanephrines, normetanephrine and metanephrine, provide a useful diagnostic test for PHEO/PGL, but this depends on appropriate reference intervals. Upper cut-offs set too high compromise diagnostic sensitivity, whereas cut-offs that are set too low can lead to false-positives. We performed a study that aimed to establish optimal reference intervals for plasma metanephrines. Blood samples were collected in the supine position from 1226 subjects, aged 5 to 84 years, including 116 children, 575 normotensive and hypertensive volunteers, and 535 patients in whom pheochromocytoma was ruled out. Reference intervals were examined according to age and gender. Various models were then examined to optimize upper cut-offs according to estimates of diagnostic sensitivity and specificity in a separate validation group of 3888 patients tested for pheochromocytoma, including 558 with confirmed disease. Plasma metanephrine, but not normetanephrine, was higher (P<0.001) in males than females, but reference intervals did not differ. Age showed a positive relationship (P<0.0001) with plasma normetanephrine and a weaker relationship (P=0.021) with metanephrine. Upper cut-offs of reference intervals for normetanephrine increased from 0.47 nmol/L in children to 1.05 nmol/L in subjects over 60 years. A non-linear model for age-adjusted compared to fixed upper cut-offs for normetanephrine, together with a higher cut-off for metanephrine (0.45 versus 0.32 nmol/L), resulted in a substantial gain in diagnostic specificity from 88.2% to 96.0% with a minimal loss in diagnostic sensitivity from 93.9% to 93.5%. These data established robust reference intervals for plasma metanephrines with age-adjusted cut-offs for normetanephrine useful for minimizing false-positive results. Hereditary PHEO/PGL Hypoxia inducible factors (HIFs) are transcription factors controlling energy, iron metabolism, erythropoiesis, and development, and, when dysregulated, contribute to tumorigenesis, cancer progression, and invasion. However, HIF-&#945; mutations have not previously been identified in any cancer. As previously mentioned, we reported two novel somatic gain-of-function HIF2A mutations in patients presenting with PGL and somatostatinoma associated with polycythemia. Both mutations showed increased HIF2A activity and protein half-life. While germline mutations of HIF-&#945; regulators, including VHL and EGLN1, have been reported in PHEOs/PGLs, this was the first report of a somatic gain-of-function mutation in HIF. Later, we reported two additional unique HIF2A mutations, which disrupt the hydroxylation domain recognized by PHD2, leading to stabilization of HIF-2&#945; and increased expression of hypoxia-related genes. In another study, we investigated the relationships between genotype-specific differences in mitochondrial function and catecholamine content in PGL tumors. Respiratory chain enzyme assays and 1H-NMR spectroscopy were performed on homogenates of sporadic PGLs and PGLs from patients with hereditary mutations in succinate dehydrogenase (SDH) subunit B (SDHB) and D (SDHD), SDH complex assembly factor 2 (SDHAF-2), VHL, rearranged during transfection (RET), neurofibromatosis type 1 (NF1), and myc-associated factor X (MAX). Imaging and PHEO/PGL We performed a study aimed at establishing the sensitivity and specificity of 18F-fluorodihydroxyphenylalanine (18F-FDOPA) PET in relation to tumor localization and the patients genetic status in a large series of PHEO/PGL patients and to discuss in detail false- negative results. A retrospective study of PHEO/PGL patients investigated with 18F-FDOPA PET or PET/CT imaging in two academic endocrine tumor centers was conducted (La Timone University Hospital, Marseilles, France and National Institutes of Health (NIH), Bethesda, MD, USA). One hundred sixteen patients (39.7% harboring germline mutations in known disease susceptibility genes) were evaluated for a total of 195 PHEO/PGL foci. 18F-FDOPA PET correctly detected 179/195 lesions (pooled sensitivity was 91.8%) in 107 patients. All but one of the sporadic tumors were 18F-FDOPA avid. 18F-FDOPA PET failed to detect 16/195 tumors in 9 patients (5 SDHD, 3 SDHB, 1 sporadic). Lesion-based sensitivities for parasympathetic PGL (head, neck, or anterior/middle thoracic), PHEO, and extra-adrenal sympathetic (abdominal or posterior thoracic) PGL were 98.2%, 93.9%, and 70.3%, respectively (P<0.001). All but 2 of the missed lesions were in the sympathetic region, and all patients with 18F-FDOPA-negative tumors had SDHx mutations. 18F-FDOPA PET failed to detect 2 head and neck PGLs (HNPGL), likely due to their small size, while most missed sympathetic PGL were larger and may have exhibited a specific 18F-FDOPA-negative imaging phenotype. 18F-FDG PET detected all the missed sympathetic lesions. We concluded that 18F-FDOPA PET appears to be a very sensitive functional imaging tool for HNPGL regardless of the genetic status of the tumors. Patients with false-negative sympathetic tumors on 18F-FDOPA PET should be tested for SDHx mutations. The potential relationship between some somatic epigenetic traits in tumors and their imaging phenotypes was also discussed. Towards better treatment of PHEO/PGL Mutations in SDHB play a crucial role in the pathogenesis of the most aggressive and metastatic PHEOs and PGLs. Although a variety of missense mutations in the coding sequence of the SDHB gene have been found in PHEOs/PGLs, it has been unclear whether these mutations impair mRNA expression, protein stability, subcellular localization, or intrinsic protein function. RT-PCR and Western blot analysis of SDHB mRNA and protein expression from SDHB-related PHEOs/PGLs demonstrated intact mRNA expression, but significantly reduced protein expression compared to non-SDHB PHEOs/PGLs. A pulse-chase assay of common SDHB missense mutations in transfected HeLa cell lines demonstrated that the loss of SDHB function was due to a reduction in mutant protein half-life, whereas co-localization of SDHB with mitochondria and immunoprecipitation with SDHA demonstrated intact subcellular localization and complex formation. The half-life of the SDHB protein increased after treatment with histone deacetylase inhibitors (HDACi), implicating the protein quality control machinery in the degradation of mutant SDHB proteins. These findings provide the first direct mechanism of functional loss resulting from SDHB mutations and suggest that reducing protein degradation with HDACi may serve as a novel therapeutic paradigm for preventing the development of SDHB-related tumors We have also suggested that targeting Hsp90 may benefit patients with advanced PHEO or PGL.